This invention relates to a raw edge type power transmission V-belt in which the tensile member in the form of a layer is displaced above or below the center line of the V-belt, and to a method of manufacturing the V-belt.
A conventional raw edge type V-belt is designated by reference numeral 11 in FIGS. 1 and 2. The conventional V-belt is, in general, manufactured according to a method in which, as shown in FIG. 1, one to several plies of rubbered bias fabric 12 are wound around a cylindrical drum or a metal mold M. A compression rubber layer 13 and an adhesion rubber layer 14 are bonded to the rubbered bias fabric 12 and a rope-shaped tensile member 15 low in elongation and high in strength is spirally wound in the form of a layer on the adhesion rubber layer 14. Another adhesion rubber layer 16 is bonded to the layer of the tensile member 15, and one to several plies of rubbered bias fabric 17 are bonded to the adhesion rubber layer 16 to obtain a belt sleeve. Then, after being heated under pressure, the belt sleeve is cut into raw edge type V-belts 11 having a predetermined width.
In this method, the belt sleeve is cut alternately obliquely as shown in FIG. 1. Therefore, the triangular material 18 between adjacent V-belts sections 11 and the end material 19 are scraps. This will increase the cost of the V-belt. Furthermore, since the tensile member 15 is embedded near the upper surface of the V-belt, the flexibility of the V-belt is reduced, and accordingly it is difficult to use the V-belt on a small diameter pulley. Thus, the conventional method is disadvantageous in these points.
In order to overcome these difficulties, another method has been proposed in the art. In the conventional method, as shown in FIG. 3, a tensile member 25 is provided along the center line of a V-belt with a cylindrical drum M being used as a mold. Adhesion rubber layers 26 and 24, compression rubber layers 27 and 23 and rubbered bias fabrics 28 and 22 are laid respectively on and under the tensile member 25 in succession, to obtain a belt sleeve. After being vulcanized, the belt sleeve is cut obliquely as shown in FIG. 3 so that V-belts having a trapezoid section and V-belts having an inverted-trapezoid section are alternately obtained. That is, a direct molded V-belt 21A as shown in FIG. 4, which can be used as it is, and an indirect molded V-belt 21B as shown in FIG. 5, which must be turned inside out before use, are alternately obtained, to reduce the number of scraps.
The method shown in FIG. 3 is superior to the method shown in FIG. 1 in that no triangular scraps 18 are created. Also, because the tensile member 15 is provided along the center line of the V-belt, the flexibility of the belt is improved, and accordingly the V-belt can be used with a small diameter pulley. However, the latter method is still disadvantageous in the following points: When the indirect molded V-belt 21B is turned inside out for use, the fabric layer 22, which was the lower part of the belt as view in FIG. 3, becomes the upper part of the belt and therefore the fabric 22 is elongated as much as 2 .pi.h. (h=the belt thickness)
Accordingly, although the direct molded V-belt is equal in dimension, configuration and structure to the indirect molded V-belt which has been turned inside out, they are different in operating characteristic as follows: When the two V-belts are run, the fabric 22 and the upper compression rubber layer 23 of the indirect molded V-belt 21B are elongated more that those of the direct molded V-belt 21A. Therefore, the fabric 22 and the upper compression rubber layer 23 of the indirect molded V-belt 21B are liable to be cracked. In addition, since the indirect molded V-belt 21B is harder than the direct molded V-belt 21A, heat is significantly generated in the indirect molded V-belt 21B and accordingly the serive life thereof is considerably shortened.